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<br />. <br /> <br />represents the lowest cost, we would only recommend this alternate <br />as a stop-gap or interim solution. There are several reasons for <br />this recommendation. With storage limitations, the utilization of <br />the reservoir for Compact administration purposes would be limited or <br />precluded. The stability of the existing dam at a storage level above <br />35,000 acre-feet is questionable. In order to provide an adequate <br />factor of safety against embankment failure, it probably will be neces- <br />sary to stabilize the dam by placing additional material on the down- <br />stream face. Stabilization of the dam would allow six feet to be <br /> <br />added to the dam crest so that the <br />capacity could be used and the dam <br />probable maximum flood. <br />Included within each of the alternates are other items of rehabili- <br /> <br />full 52,000 acre-foot <br />could safely pass the <br /> <br />storage <br />one-half <br /> <br />.' <br /> <br />tation work. It is necessary to replace the seals on the outlet gates <br />and to replace damaged concrete in the outlet gate area. A seepage <br />monitoring program would be developed whereby seepage through the north <br />abutment would be measured and monitored. Water levels would be <br />monitored to define the phreatic water level in the dam. Additional <br />test holes would be drilled in the north abutment to ascertain the <br />stability of the slope. <br />In conclusion, we have recommended that the San Luis Valley <br />Irrigation District implement the alternate whereby the dam would be <br />stabilized and rehabilitated to safely pass the one-half probable <br />maximum flood. At an estimated cost of $1.04 million, we recommend <br />that the San Luis Valley Irrigation District determine the feasibility <br />of obtaining a grant from the State of Colorado. The justifications <br />for a grant are as follows: (1) the State of Colorado currently <br />utilizes Rio Grande Reservoir to administer the Rio Grande Compact; <br />(2) 50 percent of the Compact stored water is released for the benefit <br />of other Colorado water users than the San Luis Valley Irrigation <br />District; and (3) Colorado residents living in cities or at other <br />locations along the Rio Grande will benefit from the flood protection <br />provided by the reservoir. <br /> <br />. <br /> <br />-6- <br />